Cysts and tubules are basic "building blocks" for epithelial organs such as the kidney, and defects in cyst and tubule formation are implicated in disorders such as autosomal dominant polycystic kidney disease. Our goal is to understand the biology of cystogenesis and tubulogenesis as it relates to development and disease. Using a well-described in vitro collagen gel system, we have shown that a central factor in cystogenesis and tubulogenesis is the exocyst, an evolutionarily conserved eight-protein complex involved in the secretory pathway. The secretory pathway is essential for proper cellular function, and the exocyst is known for mediating the targeting and docking of vesicles carrying secretory and basolateral proteins during the final stage of this pathway. We recently showed that the exocyst, particularly the Sec10 component, also has the novel and unexpected function of specifically regulating protein synthesis, the first stage of the secretory pathway, by interacting with the Sec61 a component of the endoplasmic reticulum (ER) translocon. In mammalian cells, proteins are simultaneously translated and translocated across the rough ER via the translocon. Our proposal is directed toward the hypothesis that the central role played by the exocyst in cyst and tubule formation is a result of its specific effects on protein synthesis. Accordingly, we will build on our findings by asking the following questions: How does the exocyst/Sec61 a interaction regulate protein synthesis? What are the interacting domains between Secl0 and Sec61a? Finally, how does the exocyst/translocon, recognize and then specifically regulate basolateral, but not apical, protein synthesis? To answer these questions we will use in vitro systems, including cell-free assays, to test whether the exocyst regulates protein translation and/or translocation (Aim 1). We will then identify and map the SeclO/Sec61 a interacting domain, and determine the functional consequences of mutating this domain, with respect to protein synthesis and cyst and tubule formation (Aim 2). Lastly, we will identify sequences that direct exocyst/translocon regulation of basolateral protein synthesis. This will be done using existing basolateral proteins that traffic to the apical membrane, due to mutations in the basolateral targeting sequence, and chimeras composed of portions of apical and basolateral proteins (Aim 3). Completion of these studies will enhance the understanding of the mechanisms of protein synthesis in cyst and tubule formation at the cellular and molecular levels and lay the groundwork for the development of novel therapeutics.